The present invention relates to a base permitting a second electric component comprising a plurality of connection fingers disposed in matrix form, for example a ball grid array (BGA), column grid array (CGA), land grid array (LGA), chip scale package (CSP) or flip-chip type integrated circuit, to be detachably attached to a first electric component, for example a printed circuit board. However, the present invention also relates to bases permitting board-to-board connections to be effected between printed circuit boards.
The technology and the production methods of integrated circuits have constantly improved during the last few years. Despite the constant improvement of the resolution used for manufacture, an increase in their surface is also being witnessed. An important problem posed by this evolution of the complexity of the integrated circuits is that of connection to other components. Currently, the number of fingers necessary may easily exceed 600. Parallel thereto, the distance between the fingers tends to be constantly reduced. A spacing of 0.5 mm between the fingers is common nowadays, while finger spacings of 0.4 and even 0.3 mm are already making their appearance.
Such VLSI circuits can turn out to be very expensive, particularly when it is a question of microprocessors used in information technology. Consequently, connection bases have been conceived which can be soldered on the paths of a printed circuit board in lieu of the integrated circuit. These connection bases are designed so that an integrated circuit can easily be plugged in and pulled out or replaced at any time. In particular, one aim of these bases is to permit the replacement of an integrated circuit comprising a large number of fingers without the risk of bending the fingers or destroying the paths or the other components of the printed circuit at the time of unsoldering.
Pin Grid Array (PGA) type circuits are tending to become more and more widespread alongside conventional PLCC type circuits. Assembly bases adapted to PGA circuits comprise a large number of contact pins disposed in the same way as the connectors of the integrated circuit. One end of the contact pins is intended to be inserted and soldered in the hole mask of the printed circuit, while the other end is configured in the form of a female connector provided with a clip and capable of receiving and establishing electrical contact with the corresponding connector of the integrated circuit.
This type of assembly base unfortunately requires considerable force for inserting and withdrawing integrated circuits comprising a large number of fingers. There is thus a risk of damaging the integrated circuit. What is more, centering the circuit above the base is not always easy, so that the fingers of the integrated circuit may bend or even break if it is attempted to insert it when it is not well centered.
The problem of connection is likewise posed with surfacemounted circuits, according to the so-called SMD technology. Known, for example, are circuits in which the fingers are disposed in matrix form (Grid Array), the fingers having the shape of part of a sphere, preferably a hemisphere. This configuration is known by the designation Ball Grid Array (BGA) or, in the case of Motorola, IMPAC (Overmold Plastic Pad Array Carrier). It is described, for example, in the German journal Megalink, Nos. 13-1995 and 17-1995, respectively, in a series of articles by Bernard Schuch entitled xe2x80x9cBall Grid Arrays (1)xe2x80x9d and xe2x80x9cBall Grid Arrays (2),xe2x80x9d respectively. The fingers of these integrated circuits are directly soldered to the contact surfaces of the printed circuit. It is very difficult afterward to remove and replace an integrated circuit, in case of a defect, for example, without risking the destruction of the printed circuit. The wastage rate of such printed circuits which can no longer be used afterward is consequently high.
Other types of connector configuration for integrated circuits have also been conceived. Column Grid Array (CGA) type circuits are similar to the BGA circuits but comprise fingers in the shape of little columns rather than in the shape of spherical sections. Also known are Land Grid Array (LGA) type circuits, chip scale packages (CSP) or still others in which the problem of mounting on the printed circuit is similarly posed.
One object of the present invention is to propose a connection base permitting an integrated circuit, for example a circuit of one of the above types, to be detachably mounted on a printed circuit board. A reliable contact must be guaranteed even when the number of connection fingers is very large, and the force to be applied for inserting or removing the circuit must be sufficiently reduced to exclude any risk of destroying the integrated circuit.
Another object of the invention is to guarantee a good-quality, homogeneous electrical contact with all the pins of the base.
According to another object of the invention, the size and particularly the thickness of the base must be as small as possible in order to permit its use in miniaturized devices as well.
According to another object of the invention, the design must be simplified or optimized to permit low-cost production, especially in the case of large-scale mass production.
Another object of the invention is to propose a base permitting board-to-board connections to be effected between different printed circuits. Thereafter, whenever it is a matter of an electric component inserted on the base, it will therefore be necessary to generalize in the case where the electric component itself is composed of a second printed circuit board. It will also be necessary to generalize, whenever it is a matter of fingers of the electric component. It will have to be understood that in the case where said component is composed of a printed circuit, fingers are likewise understood to mean the paths of this printed circuit.
These objects are achieved according to the invention by means of a base permitting a second electric component, for example an integrated circuit, comprising a plurality of connection fingers, to be detachably attached to a first electric component, for example a printed circuit board, comprising a support held between the two electric components and provided with a plurality of through openings disposed in the same way as said connection fingers, a plurality of pins extending substantially perpendicular to the support. One end of each pin is intended to be placed in electrical contact with at least one connection element of the first electric component, while the other end is intended to be placed in electrical contact with a connection element of the second electric component mounted. A pin is disposed in each of said through openings and held longitudinally only loosely within said through openings. A space is contrived between one end of each pin and the corresponding connection element of the first electric component, and/or between the other end of each pin and the corresponding connection element of the second electric component mounted. An electrically conductive compressible element is housed in at least one of said space or spaces, so as to permit an electrical contact between each pin and the corresponding connection element of the first electric component and/or the corresponding connection element of the second electric component mounted.
No particular means are provided for longitudinally holding the pins inserted in the openings very fixedly, so that the thickness of the base may be minimized. The pins are held in the holes either by stops limiting the movement without totally preventing it, or by friction on the side surfaces, for example. In the case where an electrically conductive compressible element, for example a spiral spring, is provided on each side of each pin, the force of each spring may be balanced by longitudinal movement of the pin in the opening, thus guaranteeing a homogeneous pressure of the springs on the connection elements of the two electric components and therefore an improved electrical contact.
The pins may be composed of an elongated element in the shape of a rod and preferably in one piece. In one variant, the pins are composed of a coil spring, itself compressible.
As already indicated, the invention is particularly adapted for a base intended to house an integrated circuit but may also be suitable for bases capable of receiving any type of electric component having an arrangement of similar fingers. The invention is moreover perfectly adapted to xe2x80x9cflip-chipxe2x80x9d type designs or to the interconnection between two printed circuit boards.
The objects of the invention are moreover achieved by means of contact plates which can be mounted at the end of the electrically conductive compressible elements. These plates may be used either with fixed-pin bases or with movable-pin bases.